1. Technical Field
The present invention relates to managing the reception of data units transmitted from a radiocommunication network to a plurality of user equipments via a plurality of common upper level channels mapped to a same common lower level channel.
2. Related Art
Many different types of radiocommunication networks exist. GSM, UMTS, LTE and LTE-advanced are non-limiting examples of such radiocommunication networks.
FIG. 1 is a block diagram showing a radiocommunication system. This may be a network structure of a 3rd generation partnership project (3GPP) long term evolution (LTE)/LTE-advanced (LTE-A). An E-UTRAN (Evolved-UMTS Terrestrial Radio Access Network) includes at least one base station (BS) 20 providing a user plane and a control plane towards a user equipment (UE) 10. The UE can be fixed or mobile and can be referred to as another terminology, such as a MS (Mobile Station), a UT (User Terminal), a SS (Subscriber Station), MT (mobile terminal), a wireless device, or the like. The BS 20 may be a fixed station that communicates with the UE 10 and can be referred to as another terminology, such as an e-NB (evolved-NodeB), a BTS (Base Transceiver System), an access point, or the like. There are one or more cells within the coverage of the BS 20. Interfaces for transmitting user traffic or control traffic can be used between BSs 20. The BSs 20 are interconnected with each other by means of an X2 interface. The BSs 20 are also connected by means of the S1 interface to the EPC (Evolved Packet Core), more specifically to the MME (Mobility Management Entity) by means of the S1-MME and to the Serving Gateway (S-GW) by means of the S1-U. The S1 interface supports a many-to-many relation between MME/S-GW 30 and the BS 20.
Hereinafter, downlink means communication from the BS 20 to the UE 10, and uplink means communication from the UE 10 to the BS 20. In downlink, a transmitter may be a part of the BS 20 and a receiver may be a part of the UE 10. In uplink, a transmitter may be a part of the UE 20 and a receiver may be a part of the BS 20.
FIG. 2 is a block diagram showing functional split between the E-UTRAN and the EPC. Slashed boxes depict radio protocol layers and white boxes depict the functional entities of the control plane. A BS hosts the following functions. (1) Functions for Radio Resource Management such as Radio Bearer Control, Radio Admission Control, Connection Mobility Control, Dynamic allocation of resources to UEs in both uplink and downlink (scheduling), (2) IP (Internet Protocol) header compression and encryption of user data stream, (3) Routing of User Plane data towards S-GW, (4) Scheduling and transmission of paging messages, (5) Scheduling and transmission of broadcast information, and (6) Measurement and measurement reporting configuration for mobility and scheduling. The MME hosts the following functions. (1) NAS (Non-Access Stratum) signaling, (2) NAS signaling security, (3) Idle mode UE Reachability, (4) Tracking Area list management, (5) Roaming and (6) Authentication. The S-GW hosts the following functions. (1) Mobility anchoring and (2) lawful interception. The PDN gateway (P-GW) hosts the following functions. (1) UE IP (internet protocol) allocation and (2) packet filtering.
FIG. 3 is a block diagram showing radio protocol architecture for a user plane. FIG. 4 is a block diagram showing radio protocol architecture for a control plane. The data plane is a protocol stack for user data transmission and the control plane is a protocol stack for control signal transmission.
Referring to FIGS. 3 and 4, a physical (PHY) layer provides information transfer services to an upper layer by using a physical channel. The PHY layer is connected with a MAC (Medium Access Control) layer, i.e., an upper layer of the PHY layer, through transport channels. Data is transferred between the MAC layer and the PHY layer through the transport channels. The transport channels are classified by how and with what characteristics data are transferred over the radio interface. Between different physical layers, i.e., the physical layer of a transmitter and the physical layer of a receiver, data is transferred through the physical channel.
There are several physical control channels used in the physical layer. A physical downlink control channel (PDCCH) may inform the UE about the resource allocation of paging channel (PCH) and downlink shared channel (DL-SCH), and hybrid automatic repeat request (HARQ) information related to DL-SCH. The PDCCH may carry the uplink scheduling grant which informs the UE about resource allocation of uplink transmission. A physical control format indicator channel (PCFICH) informs the UE about the number of OFDM symbols used for the PDCCHs and is transmitted in every subframe. A physical Hybrid ARQ Indicator Channel (PHICH) carries HARQ ACK/NACK signals in response to uplink transmissions. A physical uplink control channel (PUCCH) carries uplink control information such as HARQ ACK/NACK in response to downlink transmission, scheduling request and channel quality indicator (CQI). A physical uplink shared channel (PUSCH) carries uplink shared channel (UL-SCH).
The functions of the MAC layer include mapping between logical channels and transport channels, and multiplexing/demultiplexing of MAC SDUs (Service Data Units) belonging to one or different logical channels into/from transport blocks (TBs) delivered to/from the PHY layer on transport channels. The MAC layer provides services to a RLC (Radio Link Control) layer through logical channels. Logical channels may be classified into two groups: control channels for the transfer of control plane information and traffic channels for the transfer of user plane information.
The functions of the RLC layer include concatenation, segmentation and reassembly of RLC SDUs. In order to guarantee various quality of services (QoSs) required by radio bearers (RBs), the RLC layer provides three operating modes: TM (Transparent Mode), UM (Unacknowledged Mode) and AM (Acknowledged Mode). The AM RLC provides error correction through automatic repeat request (ARQ) scheme.
The functions of a PDCP (Packet Data Convergence Protocol) layer for the user plane include transfer of user data, header compression/decompression and ciphering/deciphering. The functions of the PDCP layer for the control plane include transfer of control plane data, and ciphering and integrity protection.
The RRC (Radio Resource Control) layer serves to control the logical channels, the transport channels and the physical channels in association with configuration, reconfiguration and release of radio bearers (RBs). A RB means a logical path provided by a first layer (i.e. PHY layer) and second layers (i.e. MAC layer, RLC layer and PDCP layer) for data transmission between a UE and a network. Configuring the RB includes defining radio protocol layers and characteristics of channels to provide a service and defining specific parameters and operation schemes. The RB may be classified into a signaling RB (SRB) and a data RB (DRB). The SRB is used as the path to transfer RRC messages in the control plane and the DRB is used as the path to transfer user data in the user plane.
A NAS (Non-Access Stratum) layer belonging to the upper layer of the RRC layer serves to perform session management and mobility management.
FIG. 5 shows an example of a radio frame structure.
Referring to FIG. 5, a radio frame includes 10 subframes, and a subframe includes 2 slots. The time used to transmit a subframe is referred to as a transmission time interval (TTI). For example, the length of a subframe is 1 ms and the length of a slot can be 0.5 ms.
One slot includes a plurality of orthogonal frequency division multiplexing (OFDM) symbols in time domain. In a normal cyclic prefix (CP), a slot includes 7 OFDM symbols, and in an extended CP, a slot includes 7 OFDM symbols.
A OFDM symbol is for expression of a symbol duration in time domain because OFDMA is used for downlink transmission in 3GPP LTE, the OFDM symbol can be regarded as a SC-FDMA symbol or symbol duration.
A resource block is a unit of resource assignment in 3GPP LTE, and it includes a plurality of consecutive subcarriers, i.e. 12 subcarriers, in a slot.
As shown in 3GPP TS 36.211 V8.5.0 (2008-12) “Evolved Universal Terrestrial Radio Access (E-UTRA); Physical Channels and Modulation (Release 8)”, a physical channel in LTE is divided into PDSCH (Physical Downlink Shared Channel), PUSCH (Physical Uplink Shared Channel) and PDSCH (Physical Downlink Control Channel) PUCCH (Physical Uplink Control Channel).
A subframe is divided into a control region and a data region in time domain. The control region comprises at most three OFDM symbols in a first slot of a subframe, and the number of OFDM symbols in the control region can be various. PDCCH is allocated to the control region, and PDSCH is allocated to the data region.
FIG. 6 shows mapping between downlink logical channels and downlink transport channels.
Referring to FIG. 6, a paging control channel (PCCH) can be mapped to a paging channel (PCH). A broadcast control channel (BCCH) can be mapped to a broadcast channel (BCD) or a downlink shared channel (DL-SCH). A common control channel (CCCH), a dedicated control channel (DCCH), a dedicated traffic channel (DTCH), a multicast control channel (MCCH) and a multicast traffic channel (MTCH) can be mapped to the DL-SCH. The MCCH and MTCH can also be mapped to a multicast channel (MCH).
Each logical channel type is defined by what type of information is transferred. A classification of logical channels is into two groups: control channels and traffic channels.
Control channels are used for transfer of control plane information. The BCCH is a downlink control channel for broadcasting system control information. The PCCH is a downlink channel that transfers paging information and is used when the network does not know the location cell of the UE. The CCCH is a channel for transmitting control information between UEs and a network and is used for UEs having no RRC connection with the network. The MCCH is a point-to-multipoint downlink channel used for transmitting multimedia broadcast multicast service (MBMS) control information from the network to the UE for one or several MTCHs and is only used by UEs that receive MBMS. The DCCH is a point-to-point bi-directional channel that transmits dedicated control information between a UE and the network and is used by UEs having an RRC connection.
Traffic channels are used for the transfer of user plane information. The DTCH is a point-to-point channel dedicated to one UE, for the transfer of user information. The DTCH can exist in both uplink and downlink. The MTCH is a point-to-multipoint downlink channel for transmitting traffic data from the network to the UE and is only used by UEs that receive MBMS.
The transport channels are classified by how and with what characteristics data are transferred over the radio interface. The BCH is broadcasted in the entire coverage area of the cell and has fixed, pre-defined transport format. The DL-SCH is characterized by support for hybrid automatic repeat request (HARQ), support for dynamic link adaptation by varying the modulation, coding and transmit power, possibility to be broadcast in the entire cell, possibility to use beamforming, support for both dynamic and semi-static resource allocation, support for UE discontinuous reception (DRX) to enable UE power saving and support for MBMS transmission. The PCH is characterized by support for UE discontinuous reception (DRX) to enable UE power saving and requirement to be broadcast in the entire coverage area of the cell. The MCH is characterized by requirement to be broadcast in the entire coverage area of the cell, support for MBMS Single Frequency Network (MBSFN) combining of MBMS transmission on multiple cells.
FIG. 7 shows mapping between downlink transport channels and downlink physical channels.
Referring to FIG. 7, a BCH can be mapped to a physical broadcast channel (PBCH). A MCH can be mapped to a physical multicast channel (PMCH). A PCH and a DL-SCH can be mapped to a physical downlink shared channel (PDSCH). The PBCH carries the BCH transport block. The PMCH carries the MCH. The PDSCH carries the DL-SCH and PCH.
A multimedia broadcast multicast service (MBMS) uses two logical channels, that is, an MCCH (i.e., a control channel) and an MTCH (i.e., a traffic channel). User data (e.g., actual voice or video) is transmitted on the MTCH. Configuration information for receiving the MTCH is transmitted on the MCCH. The MTCH and the MCCH are point-to-multipoint downlink channels for a plurality of UEs and can be regarded as common channels. In the MBMS, an amount of allocated radio resources does not coincide with the number of UEs receiving services. Instead, only radio resources for the common channels are allocated and the common channels are simultaneously received by the plurality of UEs, thereby improving efficiency of the radio resources.
From the above description, it can be easily understood that transmission of data units from a radiocommunication network to a plurality of UEs via a plurality of common upper level channels mapped to a same common lower level channel is possible. This is the case, for example, when a plurality of common logical channels are mapped to a same common transport channel, although other types of channels might be considered instead. For instance, a plurality of MCCH and/or MTCH channels may be mapped onto one DL-SCH channel or one MCH channel as discussed earlier.
In order for a UE to be able to identify the common logical channel on which it receives data units from the radiocommunication network at a certain point in time, a specific mechanism must take place beforehand.
According to the prior art, before transmitting data units, the radiocommunication network signals a common channel identifier for each common upper level to a group of UEs via a common control channel. Then, whenever transmitting a data unit on a common upper level channel, the network adds the common channel identifier to the data unit. When a UE receives the transmitted data unit, it identifies the common upper level channel based on said added common channel identifier.
As an example, in the context of multicast services, it is known for the radiocommunication network to transmit an RRC message on an MCCH channel for example. This RRC message includes a list of service identifiers and a corresponding list of MTCH identifiers (one MTCH being generally used with respect to one respective multicast service).
Then, each MAC PDU (Protocol Data Unit) transmitted on an MCH channel by the radiocommunication network includes a MAC header. This MAC header includes an LCID (Logical Channel Identifier) field identifying a given MTCH among all MTCHs mapped to said MCH. To this end, the LCID field includes a corresponding MTCH identifier.
On reception of a MAC PDU, a UE can then retrieve the MTCH identifier from the incorporated LCID, and thus identify the relevant MTCH.
A disadvantage of this conventional art is that the radiocommunication network must signal the list of identifiers for all common upper level channels (e.g. MTCH) mapped to the same common lower level channel (e.g. MCH). This results in signaling overhead and radio resource waste.
An object of the present invention is to limit this disadvantage.